How to Prevent Galling in Stainless Steel Fasteners
You torque a 316 stainless bolt to spec, hear a high-pitched scream, and the nut fuses to the thread — seized solid, ruining the bolt and the hole. This is galling, and it is the most frustrating failure mode in stainless fastener assembly. It happens to every engineer who over-tightens two stainless surfaces together without lubrication, and the cost in damaged parts and lost assembly time is far higher than the anti-seize compound that would have prevented it.
The short answer: galling is cold-welding of two like stainless surfaces under pressure. Prevent it by (1) never running two 316 nuts together dry, (2) using anti-seize or PTFE coating, (3) slowing the tightening speed, and (4) considering a dissimilar-grade pair (316 bolt + 304 nut).
Why stainless galling happens
Austenitic stainless steel (304, 316) is non-galling on its own — but when two like stainless surfaces slide under pressure, the chromium-oxide film breaks down and the fresh metal beneath cold-welds at the microscopic level. The nut does not spin freely; it micro-welds to the thread flank on every revolution, and each weld rips out a fragment of the thread surface. Within a few turns, the surfaces seize solid.
The problem gets worse with:
Higher torque and slower speed — pressure + heat accelerates the weld.
Dry (unlubricated) threads — no film between the two surfaces.
Fine threads and full contact — more flank surface area = more welding points.
Two austenitic grades together — 316-on-316 is the worst case; 304-on-304 is also bad.
Which grades gall the worst
| Fastener combination | Galling risk | Prevention needed |
|---|---|---|
| 316 bolt + 316 nut, dry | Very high | Mandatory anti-seize |
| 304 bolt + 304 nut, dry | High | Anti-seize recommended |
| 316 bolt + 304 nut, dry | Moderate | Lubricate for critical joints |
| Stainless bolt + zinc-plated steel nut | Low | None needed |
| 410 martensitic + 316 austenitic | Low | None needed |
| 316 + PTFE-coated thread | Very low | Built-in prevention |
The five fixes that actually work
1. Anti-seize compound. Copper-based or nickel-based anti-seize applied sparingly to the thread flanks breaks the metal-to-metal contact. Re-torque after 24 hours because the lubricant changes the preload by 20–30%.
2. PTFE-coated fasteners. Factory-applied PTFE (Teflon) coating provides a dry lubricant that survives assembly and disassembly. Toprecision supplies PTFE-coated 304/316 screws in M3–M12 for food and chemical equipment.
3. Dissimilar-grade pairing. Use a 316 bolt with a 304 nut, or a stainless bolt with a zinc-plated nut. The metallurgical difference breaks the cold-welding cycle. The corrosion trade-off is acceptable if the joint is indoors.
4. Slower tightening speed. Impact guns at high RPM are the #1 cause of galling in production. A torque wrench or pulse tool at 30 RPM generates less frictional heat and gives the chromium film time to stay intact.
5. Thread lubricant (molybdenum disulfide). MoS₂ dry film lubricant on the thread flanks reduces the friction coefficient to 0.10–0.12, which both prevents galling and tightens more consistently.
Toprecision supplies PTFE-coated and MoS₂-lubricated stainless fasteners in 304 and 316, plus dissimilar-grade bolt/nut pairs for marine and chemical equipment. Send the assembly torque and speed — we will recommend the coating and pairing that eliminates galling on your line. Request a galling-prevention consult with sample friction-coefficient test data.
